The big advantage is that it is a much smaller change than something new.
smaller changes reducing risk
the smaller amount of resources needed to get to SDL2
I think we're talking at cross purposes, because what I'm arguing
against (supporting SDL 1 and 2 at the same time) requires *more*
resources, not less. You have to expend the effort to make SDL 2 work
either way, but with your proposal, you must also expend extra effort to
ensure that SDL 1 still works, and still more effort to build the mechanisms to switch between them at build time.
SDL1 using people can keep with that for the time being
My proposal is that people who need to stick with SDL 1 will install pygame <2. We can either declare it finished and let people rely on the last working release, or make occasional 1.9.x releases to fix critical bugs. Either way, that seems less effort that trying to carry SDL 1 support forwards with us as we support SDL 2. Pygame 1.9.3 works well enough for lots of games, and I'm fine with saying that we're leaving SDL 1 support there.